feat(tanstackstart-react): Add E2E test for tunnel route

Add tunnel route and E2E test to verify createSentryTunnelRoute functionality.
The test ensures the tunnel endpoint returns 200 and correctly forwards envelopes.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: cursoragent

dev-packages/e2e-tests/test-applications/tanstackstart-react/src/routes/api.tunnel.ts

@@ -0,0 +1,8 @@
+import { createFileRoute } from '@tanstack/react-router';
+import { createSentryTunnelRoute } from '@sentry/tanstackstart-react';
+
+export const Route = createFileRoute('/api/tunnel')({
+  server: createSentryTunnelRoute({
+    allowedDsns: [process.env.E2E_TEST_DSN || ''],
+  }),
+});

dev-packages/e2e-tests/test-applications/tanstackstart-react/tests/tunnel.test.ts

@@ -0,0 +1,66 @@
+import { expect, test } from '@playwright/test';
+import { waitForError } from '@sentry-internal/test-utils';
+
+test('Tunnel route forwards envelopes to Sentry', async ({ baseURL }) => {
+  const errorEventPromise = waitForError('tanstackstart-react', errorEvent => {
+    return errorEvent?.exception?.values?.[0]?.value === 'Test error for tunnel route';
+  });
+
+  const dsn = process.env.E2E_TEST_DSN || '';
+  const [protocol, rest] = dsn.split('://');
+  const [auth, hostAndPath] = rest.split('@');
+  const [publicKey] = auth.split(':');
+  const [host, ...pathParts] = hostAndPath.split('/');
+  const projectId = pathParts[pathParts.length - 1];
+
+  const envelope = [
+    JSON.stringify({ event_id: crypto.randomUUID(), sent_at: new Date().toISOString() }),
+    JSON.stringify({
+      type: 'event',
+      length: 0,
+    }),
+    JSON.stringify({
+      exception: {
+        values: [
+          {
+            type: 'Error',
+            value: 'Test error for tunnel route',
+          },
+        ],
+      },
+      platform: 'javascript',
+      sdk: {
+        name: 'sentry.javascript.tanstackstart-react',
+        version: '0.0.0',
+      },
+      timestamp: Date.now() / 1000,
+    }),
+  ].join('\n');
+
+  const tunnelUrl = `${baseURL}/api/tunnel`;
+  const sentryUrl = `${protocol}://${host}/api/${projectId}/envelope/`;
+
+  const response = await fetch(tunnelUrl, {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/x-sentry-envelope',
+      'X-Sentry-Auth': `Sentry sentry_key=${publicKey}, sentry_version=7`,
+    },
+    body: `${sentryUrl}\n${envelope}`,
+  });
+
+  expect(response.status).toBe(200);
+
+  const errorEvent = await errorEventPromise;
+
+  expect(errorEvent).toMatchObject({
+    exception: {
+      values: [
+        {
+          type: 'Error',
+          value: 'Test error for tunnel route',
+        },
+      ],
+    },
+  });
+});